Many applications exist today in which a need arises for detecting the presence of both ferrous and non-ferrous metal objects in non-metallic materials like, for example, food products, cereal grains, forest by-products used in the manufacture of building materials, chemicals and even finished goods. Generally speaking, these applications all involve the detection of unwanted contaminants which, if left undetected, could give rise to lawsuits or, perhaps, significant damage to delicate machinery downstream of the metal detection apparatus.
Other situations exist where the ferrous metal or stainless steel object is not a contaminant at all, but rather, a necessary part of an assembly. It becomes important to know, therefore, that the part is there and that it is in the right location, or both. An example might be a plastic or non-ferrous metal part assembled automatically containing a critical ferrous metal spring that may even be hidden from view and, therefore, impossible to locate visually.
Fortunately, metal detection systems already exists which are reasonably effective in recognizing, and oftentimes even removing, metal contaminants contained within non-metallic materials regardless of whether the contaminant is a ferrous or a non-ferrous metal. Such systems frequently include a transmitter coil and a pair of receiver coils placed in close proximity to the latter. The transmitter coil puts out a high frequency signal which is altered sufficiently in the presence of a metal object moving relative thereto, regardless of whether it is of a ferrous or a non-ferrous material, such that the resultant change it undergoes can be picked up by the receiver coils which then initiate some remedial action.
The problem with detectors of this type is that no metal object can be located within approximately a yard of the detection coils without it being subject to false signals indicating the presence of the metal being detected. This means, of course, that the system is incapable of finding a metal object in, for example, a food product packaged in an aluminum container passing through the aperture. As a matter of fact, these systems cannot be used with metal chutes or ducts, most especially those in which the metal carrier is interposed between the detection apparatus and the product being tested.
In my copending application Ser. No. 177,358, filed April, 1988 . I disclose a system for detecting the presence of ferrous metal contaminants in non-metallic materials being moved on or in magnetically transparent, but stationary, metal carriers; however, even this system, unique as it is, is ill-suited for use in the detection of ferrous metal and/or stainless steel ones contained within a non-ferrous metal object of some description like an aluminum pan or a metal object cast or otherwise made from a magnetically-transparent metal. An even greater problem exists in differentiating between like metals in a product, i.e. a ferrous metal part present in a ferrous metal assembly.
Accordingly, an urgent need exists for a metal detection system which can, in fact, reliably discriminate between ferrous and non-ferrous metals; like metals in the same product, either ferrous or non-ferrous; or even the position of a metal part or object within an assembly made of a dissimilar material, metal or otherwise.
1. Field of the Invention
The present invention relates, therefore, to a novel method and apparatus for discriminating between the same or different metals in the same product. The invention is also capable of detecting the amount or location or both of a one metal with respect to another which differs therefrom in its magnetic properties.
2. Description of the Related Art
The closest and most pertinent prior art known to applicant is that mentioned above which comprises a transmitting coil operative to generate a field in the area through which the product being tested must pass and a pair of detector coils which are responsive to any disturbance in this field due to the presence of metal objects and operative to set off an alarm or initiate some other corrective action. Insofar as applicant is aware, no system yet exists which is capable of differentiating between like or unlike metal materials in the way his does nor is any prior art magnetic system known to him which is capable of telling whether a given metal, be it magnetic or otherwise, is present in the proper proportions. There are, of course, systems which weigh an object, X-ray it, test the shape thereof or otherwise analyze one or more of its properties, dimensions or other of its parameters in order to ascertain whether or not it meets specifications; however, none of these prior art systems, at least insofar as applicant is aware, involves as his does using the deflection taking place in a generator of a magnetic field mounted atop a load cell as a reliable and accurate indication of some anomaly in the product being tested. The detection of conductive metals requires that they move relative to the magnetic field; whereas, those which are used in the detection of ferrous materials are effective regardless of whether the object being tested is moving or standing still.
Applicant is also aware of certain U.S. patents which employ generators of magnetic or electromagnetic fields which generate an output signal in response to the presence or movement of an outside instrumentality. The Okubo U.S. Pat. No. 4,314,202 senses the flexural vibration of a structural member located within the field while the Junker et al U.S. Pat. No. 4,528,856 generates a signal measuring the stress in a magnetic workpiece. Neither of these systems has as their objective that of metal detection nor would they function on such an application without complete redesign. U.S. Pat. No. 4,310,797 is somewhat more pertinent in that it relates to a so-called "stud finder" which employs a permanent magnet responsive to the presence of a ferrous metal object to close a switch and turn on a light. While the magnet does move in the presence of a ferrous metal part, no load-responsive element is a part of the combination. Finally, the Smirnov U.S. Pat. No. 4,232,265 is the most pertinent in that it employs two ferromagnetic plates, one fixed and the other movable with the movable one being mounted upon a strain gauge. The intensity of the interfering fields is quantified by the output signal keyed to the movement of the strain gauge. Here again, the application for which the system is designed is one of measuring the intensity between two interacting magnetic fields in a bench-type fixed system, not an industrial environment where the products are oftentimes moving, are rarely if ever ferromagnetic and may not even include a ferrous metal although capable of sensing the presence of a conductive one.